Multiplexer with acoustic wave resonators

ABSTRACT

Embodiments of this disclosure relate to multiplexers that include acoustic wave filters for filtering radio frequency signals. In certain embodiments, a multiplexer includes a first acoustic wave filter including bulk acoustic wave resonators and a second acoustic wave filter including multilayer piezoelectric substrate surface acoustic wave resonators. The second acoustic wave filter can have a second pass band that is above a first pass band of the first acoustic wave filter. Related acoustic filter assemblies, packaged radio frequency modules, wireless communication devices, and methods are disclosed.

CROSS-REFERENCE TO RELATED APPLICATION

Any and all applications for which a foreign or domestic priority claimis identified in the Application Data Sheet, or any correction thereto,are hereby incorporated by reference under 37 CFR 1.57.

BACKGROUND Technical Field

Embodiments of this disclosure relate to multiplexers with filters thatinclude acoustic wave resonators.

Description of Related Technology

Acoustic wave filters can be implemented in radio frequency electronicsystems. For instance, filters in a radio frequency front end of amobile phone can include acoustic wave filters. An acoustic wave filtercan be a band pass filter. A plurality of acoustic wave filters can bearranged as a multiplexer. For example, two acoustic wave filters can bearranged as a duplexer.

An acoustic wave filter can include a plurality of acoustic waveresonators arranged to filter a radio frequency signal. Example acousticwave filters include surface acoustic wave (SAW) filters and bulkacoustic wave (BAW) filters. Designing multiplexers with acoustic wavefilters to meet performance specifications with low loss can bechallenging.

SUMMARY OF CERTAIN INVENTIVE ASPECTS

The innovations described in the claims each have several aspects, nosingle one of which is solely responsible for its desirable attributes.Without limiting the scope of the claims, some prominent features ofthis disclosure will now be briefly described.

One aspect of this disclosure is a multiplexer with acoustic wavefilters for filtering radio frequency signals. The multiplexer includesa first acoustic wave filter having a first pass band and a secondacoustic wave filter coupled to the first acoustic wave filter at acommon node. The first acoustic wave filter includes bulk acoustic waveresonators. The second acoustic wave filter having a second pass bandwith a frequency range above the first pass band. The second pass bandis associated with a different frequency band than the first pass band.The second acoustic wave filter includes multilayer piezoelectricsubstrate surface acoustic wave resonators.

The bulk acoustic wave resonators have spurious modes below the firstpass band. The bulk acoustic wave resonators can have spurious modesbelow the first pass band, and the multilayer piezoelectric substratesurface acoustic wave resonators can have a gamma of at least 0.85 inthe first pass band. Spurious modes of the bulk acoustic wave resonatorscan be outside of the second pass band. The bulk acoustic waveresonators can have a substantially constant gamma in the second passband.

The multilayer piezoelectric substrate surface acoustic wave resonatorscan have a gamma of at least 0.85 in the first pass band.

The multiplexer can further include a third acoustic wave filter coupledto the common node and having a third pass band, in which the third passband is between the first pass band and the second pass band. The thirdacoustic wave filter can be a bulk acoustic wave filter. The thirdacoustic wave filter can be a surface acoustic wave filter. The thirdacoustic wave filter can be a multilayer piezoelectric substrate surfaceacoustic wave filter. The third acoustic wave filter can be atemperature compensated substrate surface acoustic wave filter.

The multiplexer can further include a third acoustic wave filter coupledto the common node and having a third pass band and a fourth acousticwave filter coupled to the common node and having a fourth pass band.The third acoustic wave filter can include second bulk acoustic waveresonators. The fourth acoustic wave filter can include secondmultilayer piezoelectric surface acoustic wave resonators. The thirdpass band can be between the first pass band and the fourth pass band.The fourth pass band can be between the third pass band and the secondpass band.

The multiplexer can further include a third acoustic wave filter coupledto the common node and having a third pass band and a fourth acousticwave filter coupled to the common node and having a fourth pass band.The first pass band and the third pass band can be associated with afirst frequency band, and the second pass band and the fourth pass bandcan be associated with a second frequency band. The common node can beconfigured to receive a carrier aggregation signal including carriersassociated with the first frequency band and the second frequency band.

The multiplexer can further include two additional acoustic wave filterscoupled to the common node, in which the first pass band being a lowestpass band of all acoustic wave filters of the multiplexer, and in whichthe second pass band being a highest pass band of all acoustic wavefilters of the multiplexer.

The multiplexer can further include four additional acoustic wavefilters coupled to the common node, in which the first pass band is alowest pass band of all acoustic wave filters of the multiplexer, and inwhich the second pass band being a highest pass band of all acousticwave filters of the multiplexer.

Another aspect of this disclosure is a wireless communication devicethat includes an antenna and a radio frequency front end including amultiplexer. The multiplexer can be any suitable multiplexer disclosedherein.

The radio frequency front can include a frequency multiplexing circuitcoupled between the common node of the multiplexer and the antenna. Thewireless communication device can further include an antenna switchcoupled between the common node of the multiplexer and the antenna.

Another aspect of this disclosure is a packaged radio frequency modulethat includes a multiplexer, a multi-throw radio frequency switchcoupled to the multiplexer, and a package enclosing the multiplexer andthe multi-throw radio frequency switch. The multiplexer can include anysuitable features of the multiplexers disclosed herein.

The packaged radio frequency module can further include a poweramplifier enclosed within the package, in which the power amplifier isconfigured to provide a radio frequency signal to the multiplexer.

The packaged radio frequency module can further include a low noiseamplifier enclosed within the package, in which the low noise amplifieris configured to receive a radio frequency signal to the multiplexer.

Another aspect of this disclosure is an acoustic wave filter assemblythat includes a bulk acoustic wave die on a substrate and a multilayerpiezoelectric substrate die on the substrate. The bulk acoustic wave dieincludes bulk acoustic wave resonators arranged as a first filter havinga first pass band. The multilayer piezoelectric substrate die includesmultilayer piezoelectric substrate surface acoustic wave resonatorsarranged as a second filter having a second pass band. The second filteris coupled to the first filter at a common node. The second pass band isassociated with a different frequency band than the first pass band.

The substrate can be a laminate substrate. The acoustic wave filterassembly can further include a package enclosing the bulk acoustic wavedie and the multilayer piezoelectric substrate die.

The acoustic wave filter assembly can further include a surface acousticwave die on the substrate, in which the surface acoustic wave dieincludes surface acoustic wave resonators arranged as a third filtercoupled to the common node. The surface acoustic wave resonators can betemperature compensated surface acoustic wave resonators. The surfaceacoustic wave resonators can be second multilayer piezoelectricsubstrate surface acoustic wave resonators.

The first filter and the second filter can be included in a multiplexerthat includes one or more suitable features of the multiplexersdisclosed herein.

Another aspect of this disclosure is a multiplexer with acoustic wavefilters for filtering radio frequency signals. The multiplexer includesa first acoustic wave filter having a first pass band and a secondacoustic wave filter coupled to the first acoustic wave filter at acommon node. The first acoustic wave filter includes type II bulkacoustic wave resonators, in which the type II bulk acoustic waveresonators have spurious modes below the first pass band. The secondacoustic wave filter have a second pass band with a frequency rangeabove the first pass band. The second acoustic wave filter includes typeI bulk acoustic wave resonators having spurious modes above the secondpass band.

The type I bulk acoustic wave resonators can have a gamma of at least0.85 in the first pass band. The type II bulk acoustic wave resonatorscan have a substantially constant gamma in the second pass band.

The multiplexer can further include a third acoustic wave filter coupledto the common node and having a third pass band, in which the third passband is between the first pass band and the second pass band.

The multiplexer can further include two additional acoustic wave filterscoupled to the common node, in which the first pass band is a lowestpass band of all acoustic wave filters of the multiplexer. Themultiplexer can support a carrier aggregation of two frequency bands.

The multiplexer can further include four additional acoustic wavefilters coupled to the common node, in which the first pass band is alowest pass band of all acoustic wave filters of the multiplexer, and inwhich the second pass band is a highest pass band of all acoustic wavefilters of the multiplexer. The multiplexer can support a carrieraggregation of three frequency bands.

Another aspect of this disclosure is a multiplexer with acoustic wavefilters for filtering radio frequency signals. The multiplexer includesa first acoustic wave filter coupled to a common node and having a firstpass band, the first acoustic wave filter including bulk acoustic waveresonators; a second acoustic wave filter coupled to the common node andhaving a second pass band; a third acoustic wave filter coupled to thecommon node and having a third pass band; and a fourth acoustic wavefilter coupled to the common node and having a fourth pass band, thefourth acoustic wave filter including surface acoustic wave resonators,the first pass band being a lowest pass band of all acoustic wavefilters of the multiplexer.

The fourth pass band can be a highest pass band of all acoustic wavefilters of the multiplexers.

The surface acoustic wave resonators can include multilayerpiezoelectric substrate surface acoustic wave resonators.

The first acoustic wave filter and third acoustic wave filter can eachinclude multilayer piezoelectric substrate surface acoustic waveresonators.

The second acoustic wave filter, third acoustic wave filter, and thefourth acoustic wave filter can each include multilayer piezoelectricsubstrate surface acoustic wave resonators.

The surface acoustic wave resonators can include temperature compensatedsurface acoustic wave resonators.

The second acoustic wave filter can include second bulk acoustic waveresonators, the third acoustic wave filter can include second surfaceacoustic wave resonators, and the second pass band can be below thethird pass band.

The second acoustic wave filter can include second bulk acoustic waveresonators, the third acoustic wave filter can include third bulkacoustic wave resonators, and the second pass band can be below thethird pass band.

The second acoustic wave filter can include second surface acoustic waveresonators, the third acoustic wave filter can include third surfaceacoustic wave resonators, and the second pass band can be below thethird pass band.

The multiplexer is configured can support a carrier aggregation of twofrequency bands.

The multiplexer can further include: a fifth acoustic wave filtercoupled to the common node and having a fifth pass band; and a sixthacoustic wave filter coupled to the common node and having a sixth passband. The multiplexer can support a carrier aggregation of threefrequency bands.

The bulk acoustic wave resonators can have spurious modes below thefirst pass band.

The surface acoustic wave resonators can have a gamma of at least 0.85in the first pass band.

The bulk acoustic wave resonators can have spurious modes below thefirst pass band, and the surface acoustic wave resonators have a gammaof at least 0.85 in the first pass band.

Spurious modes of the bulk acoustic wave resonators can be outside ofthe fourth pass band.

The bulk acoustic wave resonators can have a substantially constantgamma in the fourth pass band.

For purposes of summarizing the disclosure, certain aspects, advantagesand novel features of the innovations have been described herein. It isto be understood that not necessarily all such advantages may beachieved in accordance with any particular embodiment. Thus, theinnovations may be embodied or carried out in a manner that achieves oroptimizes one advantage or group of advantages as taught herein withoutnecessarily achieving other advantages as may be taught or suggestedherein.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of this disclosure will now be described, by way ofnon-limiting example, with reference to the accompanying drawings.

FIG. 1A is a schematic block diagram of a duplexer according to anembodiment.

FIG. 1B is a graph of transmission characteristics over frequency forfilters of the duplexer of FIG. 1A.

FIG. 2A is a schematic block diagram of a quadplexer according to anembodiment.

FIG. 2B is a graph of transmission characteristics over frequency forfilters of the quadplexer of FIG. 2A.

FIG. 3A is a graph of transmission characteristics over frequency forfilters of the quadplexer of FIG. 2A compared to standalone filters.

FIG. 3B is a graph of gamma over frequency for the quadplexer of FIG. 2Awith bulk acoustic wave (BAW) filters having pass bands below pass bandsof a multilayer piezoelectric substrate (MPS) surface acoustic wave(SAW) filters.

FIG. 4A is a graph of transmission characteristics over frequency for aquadplexer compared to standalone filters.

FIG. 4B is a graph of gamma over frequency for the quadplexercorresponding to FIG. 4A.

FIG. 5A is a graph of transmission characteristics over frequency for aquadplexer compared to standalone filters.

FIG. 5B is a graph of gamma over frequency for the quadplexercorresponding to FIG. 5A.

FIG. 6A is a schematic block diagram of a duplexer according to anembodiment.

FIG. 6B is a schematic block diagram of a duplexer according to anotherembodiment.

FIG. 6C is a schematic block diagram of a duplexer according to anotherembodiment.

FIG. 7A is a schematic block diagram of a quadplexer according to anembodiment.

FIG. 7B is a schematic block diagram of a quadplexer according toanother embodiment.

FIG. 8 is a schematic block diagram of a quadplexer according to anotherembodiment.

FIG. 9A is a schematic block diagram of a quadplexer according toanother embodiment.

FIG. 9B is a schematic block diagram of a quadplexer according toanother embodiment.

FIG. 9C is a schematic block diagram of a quadplexer according toanother embodiment.

FIG. 10A is a schematic block diagram of a multiplexer according to anembodiment.

FIG. 10B is a schematic block diagram of a multiplexer according toanother embodiment.

FIG. 11A is a cross sectional view of an MPS SAW resonator according toan embodiment.

FIG. 11B is a cross sectional view of a SAW resonator according to anembodiment.

FIG. 11C is a cross sectional view of a temperature compensated SAWresonator according to an embodiment.

FIG. 12 is a cross sectional view of a bulk acoustic wave resonatoraccording to an embodiment.

FIG. 13 is a schematic diagram of a ladder filter according to anembodiment.

FIG. 14 is a schematic diagram of a radio frequency system that includesquadplexers coupled to an antenna by way of a diplexer.

FIG. 15 is a schematic diagram of a radio frequency system that includesa quadplexer coupled to an antenna.

FIG. 16 is a schematic diagram of a radio frequency system that includesan antenna coupled to receive paths by way of a multiplexer.

FIG. 17A is a schematic diagram of a radio frequency system thatincludes multiplexers in signal paths between power amplifiers and anantenna.

FIG. 17B is a schematic diagram of another radio frequency system thatincludes multiplexers in signal paths between power amplifiers and anantenna.

FIG. 18A is a block diagram that illustrates different die that includeacoustic wave resonators of filters of a multiplexer according to anembodiment.

FIG. 18B is a block diagram that illustrates different die that includeacoustic wave resonators of filters of a multiplexer according to anembodiment.

FIG. 18C is a block diagram that illustrates different die that includeacoustic wave resonators of filters of a multiplexer according to anembodiment.

FIG. 19 is a schematic block diagram of a module that includes a poweramplifier, a switch, and a multiplexer according to an embodiment.

FIG. 20 is a schematic block diagram of a module that includes poweramplifiers, switches, and a multiplexer according to an embodiment.

FIG. 21A is a schematic block diagram of a wireless communication devicethat includes a multiplexer according to an embodiment.

FIG. 21B is a schematic block diagram of a wireless communication devicethat includes a multiplexer according to an embodiment.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

The following description of certain embodiments presents variousdescriptions of specific embodiments. However, the innovations describedherein can be embodied in a multitude of different ways, for example, asdefined and covered by the claims. In this description, reference ismade to the drawings where like reference numerals can indicateidentical or functionally similar elements. It will be understood thatelements illustrated in the figures are not necessarily drawn to scale.Moreover, it will be understood that certain embodiments can includemore elements than illustrated in a drawing and/or a subset of theelements illustrated in a drawing. Further, some embodiments canincorporate any suitable combination of features from two or moredrawings.

Surface acoustic wave (SAW) and bulk acoustic wave (BAW) technologiesare both capable of achieving relatively high impedance valuesout-of-band. Certain high performance BAW filters can outperform SAWfilters in terms of out-of-band impedance magnitude over a widerfrequency span. At the same time, BAW filters can be suited to filtersignals having frequencies up to about 10 gigahertz (GHz). BAW filterscan achieve relatively low insertion loss and desirable rejection ofadjacent frequency bands. On the other hand, SAW filters can be lowercost than BAW filters. SAW filters include, for example, multilayerpiezoelectric substrate (MPS) SAW filters, temperature compensated SAW(TCSAW) filters, and non-temperature compensated SAW filters. However,SAW filters can encounter difficulty filtering signals at relativelyhigh frequencies, such as frequencies above about 2.7 GHz, in certainapplications. Given these differences in technology, SAW filters can beused for filtering relatively lower frequencies than BAW filters in avariety of applications and thereby save costs.

Low loss multiplexer devices are desired for relatively complex radiofrequency (RF) systems for mobile communication. A multiplexer caninclude band pass filters coupled together at a common node. Insertionloss of a filter in the multiplexer is typically degraded compared tostandalone filters due to loading from other filters of the multiplexer.This disclosure provides low loss multiplexers that include a bulkacoustic wave (BAW) filter and a multilayer piezoelectric substrate(MPS) SAW filter. An MPS SAW filter can be referred to as an MPS filter.Other low loss multiplexers are disclosed.

Low insertion loss can be difficult to achieve in a multiplexer thatincludes a plurality of filters. This can be due to loading. To addressloading problems, multiplexers with a BAW filter and an MPS SAW filterare disclosed. By setting the pass band of the BAW filter to a lowerfrequency than the pass band of the MPS SAW filter, loading can bereduced and/or almost eliminated. The BAW filter can achieve desirablegamma for higher frequencies and the MPS SAW filter can achievedesirable gamma for lower frequencies. Gamma is a reflectioncoefficient. A multiplexer with a BAW filter having the lowest pass bandof all filters of the multiplexer and an MPS SAW filter having thehighest pass band of all filters of the multiplexer can achieve lowloading loss and low insertion loss for the multiplexer. Other types ofSAW filters (e.g., a temperature compensated SAW filter) can beimplemented in place of the MPS SAW filter and achieve relatively lowinsertion loss for filters in a multiplexer in certain instances.

FIG. 1A is a schematic block diagram of a duplexer 10 according to anembodiment. The illustrated duplexer 10 includes a BAW filter 12 and anMPS filter 14. The BAW filter 12 and the MPS filter 14 are band passfilters coupled together at a common node COM. The BAW filter 12 iscoupled between a first RF node RF1 and the common node COM. The BAWfilter 12 includes BAW resonators. The BAW resonators can be film bulkacoustic wave resonators (FBARs). In some other applications, the BAWresonators can include solidly mounted resonators (SMRs). The MPS filter14 is coupled between a second RF node RF2 and the common node COM. TheMPS filter 14 includes MPS SAW resonators. For example, all acousticwave resonators of the MPS filter 14 can be MPS SAW resonators. MPS SAWresonators can include layered substrate SAW resonators and/or bondedsubstrate SAW resonators. The BAW filter 12 and the MPS filter 14 can beassociated with the same frequency band in certain instances, in whichone filter is a transmit filter and the other filter is a receivefilter. The BAW filter 12 and the MPS filter 14 can be associated withdifferent frequency bands in some instances, such as in diversityreceive applications and/or in any other suitable applications in whichfiltering of different bands in a duplexer is desired. The BAW filter 12and the MPS filter 14 can be associated with different frequencysub-bands within the same frequency band in some instances.

FIG. 1B is a graph of transmission characteristics over frequency forfilters of the duplexer 10 of FIG. 1A. FIG. 1B illustrates a first passband 16 of the BAW filter 12 and a second pass band of the MPS filter14. As illustrated, the second pass band 18 spans a frequency rangeabove the first pass band 16. As also illustrated in FIG. 1B, the firstpass band 16 spans a frequency range below the second pass band 18.

Referring back to FIG. 1A, the BAW filter 12 can have the first passband 16 and a first stop band above the first pass band 16. In the firststop band, the frequency response of the BAW filter 12 can be relativelyclean. The BAW filter 12 can include type II BAW resonators that havespurious modes below their respective resonant frequencies. Accordingly,spurious modes of the BAW filter 12 can be outside of the second passband 18 of the MPS filter 14. The MPS filter 14 can have the second passband 18 and a second stop band below second pass band 18. In the secondstop band, the frequency response of the MPS filter 14 can be relativelyclean. MPS SAW resonators of the MPS filter 14 can have spurious modesabove their respective resonant frequencies. Accordingly, spurious modesof the MPS filter 14 can be outside of the first pass band 16 of the BAWfilter 12.

The duplexer 10 can be a relatively loss low duplexer due to thespurious modes of the BAW filter 12 being outside of the second passband 18 of the MPS filter 14 and the spurious modes of the MPS filter 14being outside of the first pass band 16 of the BAW filter 12.

Multiplexers with more filters coupled to common node can have moresignificant technical challenges related to loading relative tomultiplexers with fewer filters coupled to a common node. For example,loading can be a more significant technical challenge to address forquadplexers than for duplexers because more filters are coupled togetherat a common node that can contribute to loading in quadplexers.Accordingly, in quadplexers, there can be more other filters that canundesirably impact insertion loss in a pass band of a particular filterthan in duplexers.

FIG. 2A is a schematic block diagram of a quadplexer 20 according to anembodiment. The quadplexer 20 includes four acoustic wave filterscoupled to a common node COM. As illustrated, the quadplexer 20 includesa first BAW filter 22, a second BAW filter 24, a first MPS filter 26,and a second MPS filter 28. The first BAW filter 22 is coupled between afirst RF node RF1 and the common node COM. The second BAW filter 24 iscoupled between a second RF node RF2 and the common node COM. The firstBAW filter 22 and the second BAW filter 24 each include BAW resonators(e.g., FBARs and/or SMRs). In an embodiment, the acoustic waveresonators of the first BAW filter 22 and the second BAW filter 24consist of FBARs. The first MPS filter 26 is coupled between a third RFnode RF3 and the common node COM. The second MPS filter 28 is coupledbetween a fourth RF node RF4 and the common node COM. The first MPSfilter 26 and the second MPS filter 28 each include MPS SAW resonators.

In certain applications, the quadplexer 20 can be similar to a firstduplexer that includes BAW filters 22 and 24 for first frequency bandand a second duplexer that includes MPS filters 26 and 28 for a secondfrequency band coupled together at the common node COM, in which thesecond frequency band is above the first frequency band.

FIG. 2B is a graph of transmission characteristics over frequency forfilters of the quadplexer 20 of FIG. 2A. FIG. 2B illustrates a firstpass band 32 of the first BAW filter 22, a second pass band 34 of thesecond BAW filter 24, a third pass band 36 of the first MPS filter 26,and a fourth pass band 38 of the second MPS filter 28. The first passband 32 of the first BAW filter 22 is lower than the pass bands of allother acoustic wave filters of the quadplexer 20. The fourth pass band38 of the second MPS filter 28 is higher than the pass bands of allother acoustic wave filters of the quadplexer 20. The second pass band34 of the second BAW filter 24 is below the third pass band 36 of thefirst MPS filter 34. Accordingly, the pass bands of each BAW filter ofthe quadplexer 20 are below the pass bands of each MPS filter of thequadplexer 20.

The BAW filters 22 and 24 can have respective stop bands above theirpass bands 32 and 34. The BAW filters 22 and 24 can be formed of type IIBAW resonators that have spurious modes below their respective resonantfrequencies. Accordingly, spurious modes of the BAW filters 22 and 24can be outside of the pass bands 36 and 38 of the MPS filters 26 and 28,respectively. The MPS filters 26 and 28 can have respective stop bandsbelow their pass bands 36 and 38. The MPS filters 26 and 28 can beformed of MPS SAW resonators that have spurious modes above theirrespective resonant frequencies. Accordingly, spurious modes of the MPSfilters 26 and 28 can be outside of the pass bands 32 and 34 of the BAWfilters 22 and 24, respectively.

FIG. 3A is a graph of transmission characteristics over frequency forfilters of the quadplexer 20 of FIG. 2A compared to standalone filters.In the quadplexer 20, BAW filters 22 and 24 have pass bands below passbands of the MPS filters 26 and 28. Insertion loss degradation cancorrespond to the reduction in transmission characteristics due toloading in the quadplexer 20. According, the graph in FIG. 3A shouldillustrate the impact of loading in the quadplexer 20 by the differencebetween the transmission characteristics for a standalone filter and thetransmission characteristics for the same filter in the quadplexer 20.FIG. 3A indicates that insertion loss degradation for BAW filters 22 and24 is relatively small. In addition, FIG. 3A indicates that insertionloss degradation is relatively small for the MPS filter 26 and 28.

FIG. 3B is a graph of gamma over frequency for the BAW filers 22 and 24and the MPS filters 26 and 28 the quadplexer 20 of FIG. 2A in which theBAW filters 22 and 24 have lower pass bands than the MPS filters 26 and28. FIG. 3B illustrates that there is relatively high gamma for the BAWfilters 22 and 24 above the pass bands of the BAW filters 22 and 24.Relatively high gamma for the BAW filters 22 and 24 is indicated at forthe respective pass bands of the MPS filters 26 and 28. The BAW filters22 and 24 can have gamma of at least 0.85 and/or at least 0.9 in thepass bands of the MPS filters 26 and 28. A maximum value of gamma canbe 1. A gamma of 1 can indicate 100% reflection. FIG. 3B illustratesthat there is relatively high gamma for the MPS filters 26 and 28 belowthe pass bands of the MPS filters 26 and 28. Relatively high gamma forthe MPS filters 26 and 28 is indicated for the respective pass bands ofthe BAW filters 22 and 24. The MPS filters 26 and 28 can have gamma ofat least 0.85 and/or at least 0.9 in the pass bands of the BAW filters22 and 24. Accordingly, the quadplexer 20 of FIG. 2A with BAW filters 22and 24 having lower pass bands than MPS filters 26 and 28 is a desirablecombination for multiplexing.

FIG. 4A is a graph of transmission characteristics over frequency for aquadplexer compared to standalone filters. The quadplexer correspondingto the graphs of FIGS. 4A and 4B includes two MPS filters and two BAWfilters, in which the MPS filters have lower pass bands than the BAWfilters. The graph of FIG. 4A indicates significant insertion lossdegradation in pass bands of the MPS filters due to loading loss.

FIG. 4B is a graph of gamma over frequency for a quadplexer with two MPSfilters having pass bands below two BAW filters. The graph of FIG. 4Bindicates that gamma for the BAW filters is degraded. The gammadegradation corresponds to pass bands of the MPS filters.

FIG. 5A is a graph of transmission characteristics over frequency for aquadplexer compared to standalone filters. The quadplexer correspondingto the graphs of FIGS. 5A and 5B includes two MPS filters and two BAWfilters, in which the MPS filters have significantly lower pass bandsthan the BAW filters. There is over 250 megahertz (MHz) between thelower edge of a BAW filter pass band an upper edge of an MPS filter passband as indicated by FIG. 5A. The graph of FIG. 5A indicates significantinsertion loss degradation in a pass band of the BAW filter with ahigher pass band.

FIG. 5B is a graph of gamma over frequency for a quadplexer with two MPSfilters having pass bands significantly below two BAW filters. The graphof FIG. 5B indicates that gamma for the MPS filters is degraded. Thegamma degradation can be due to loading loss resulting from higher orderspurious responses of the MPS filters. The gamma degradation correspondsto the pass band of the BAW filter with the higher pass band.

Based on the above simulation results, it can be desirable for aquadplexer to include (a) filters for a lower frequency band withspurious responses below the pass bands and (b) filters for a higherfrequency band with relatively high gamma below the pass band. Thefilters for the lower frequency band can include a transmit filter and areceive filter. The filters for the lower frequency band can include aBAW filter. The filters for the higher frequency band can include atransmit filter and a receive filter. The filters for the higherfrequency band can include one or more of an MPS filter, a SAW filter, aTCSAW filter, or a type I BAW filter.

Although the duplexer 10 of FIG. 1A and the quadplexer 20 of FIG. 2Ainclude a BAW filter and an MPS filter, the principles and advantagesdisclosed herein can be applied to other types of filters with certaincharacteristics of the filters of the duplexer 10 of FIG. 1A and thequadplexer 20 of FIG. 2A. For example, a filter with a lowest pass bandin a multiplexer can have spurious modes below its pass band. Such afilter can be a type II BAW filter. As another example, a filter with ahighest pass band of a multiplexer can have relatively high gamma belowits pass band. Such a filter can be an MPS filter, a SAW filter, a TCSAWfilter, or a type I BAW filter. In certain applications, a multiplexercan include at least one acoustic wave filter with two or more differenttypes of acoustic wave devices implemented with frequency domaincharacteristics of a filter of the duplexer 10 and/or a filter of thequadplexer 20.

FIGS. 6A to 6C illustrate duplexers with a BAW filter having a firstpass band that is below a second pass band of another type of acousticwave filter. The other acoustic wave filter can be associated with thesame frequency band as the BAW filter (e.g., the filters can be foruplink and downlink signals of the same frequency band). In some otherapplications, the BAW filter and the other acoustic wave filter can havepass bands associated with different frequency bands.

FIG. 6A is a schematic block diagram of a duplexer 60 according to anembodiment. As illustrated, the duplexer 60 includes a BAW filter 12 anda SAW filter 62 coupled to each other at a common node COM. The BAWfilter 12 has a first pass band that is below a second pass band of theSAW filter 62. The duplexer 60 is like the duplexer 10 of FIG. 1A,except that a SAW filter 62 is implemented in place of the MPS filter14. The SAW filter 62 includes SAW devices, such as SAW resonators. TheSAW resonators can be any suitable SAW resonators, including withoutlimitation TCSAW resonators, non-temperature compensated SAW resonators,or MPS SAW resonators.

FIG. 6B is a schematic block diagram of a duplexer 63 according to anembodiment. As illustrated, the duplexer 63 includes a BAW filter 12 anda TCSAW filter 64 coupled to each other at a common node COM. The BAWfilter 12 has a first pass band that is below a second pass band of theTCSAW filter 64. The duplexer 63 is like the duplexer 10 of FIG. 1A,except that a TCSAW filter 64 is implemented in place of the MPS filter14. The TCSAW filter 64 includes TCSAW resonators.

FIG. 6C is a schematic block diagram of a duplexer 65 according to anembodiment. As illustrated, the duplexer 65 includes a type II BAWfilter 67 and a type I BAW filter 68 coupled to each other at a commonnode COM. The type II BAW filter 67 has a first pass band that is belowa second pass band of the type I BAW filter 68. The type II BAW filter67 includes BAW resonators that have spurious modes below their resonantfrequencies. The type I BAW filter 68 includes BAW resonators that havespurious modes above their resonant frequencies.

FIGS. 7A and 7B illustrate quadplexers with a BAW filter having a lowestpass band of the filters of the quadplexer and an MPS filter having ahighest pass band of the filters of the quadplexer. The filters with themiddle pass bands of the quadplexers are implemented by different typesof acoustic wave filters than the quadplexer 20 of FIG. 2A.

FIG. 7A is a schematic block diagram of a quadplexer 70 according to anembodiment. The quadplexer 70 is like the quadplexer 20 of FIG. 2Aexcept that the MPS filter 26 of the quadplexer 20 is replaced by theBAW filter 72 in the quadplexer 70.

FIG. 7B is a schematic block diagram of a quadplexer 73 according toanother embodiment. The quadplexer 73 is like the quadplexer 20 of FIG.2A except that the BAW filter 24 of the quadplexer 20 is replaced by theMPS filter 74 in the quadplexer 73.

FIG. 8 is a schematic block diagram of a quadplexer 80 according toanother embodiment. The quadplexer 80 includes a BAW filter 22, a firstTCSAW filter 82, a second TCSAW filter 84, and an MPS filter 28. The BAWfilter 22 has a lowest pass band of the filters of the quadplexer 80.The MPS filter 28 has a highest pass band of the filters of thequadplexer 80. The filters with the middle pass bands of the quadplexer80 are implemented by TCSAW resonators in the quadplexer 80. Thequadplexer 80 is an example of a quadplexer in which a different type ofacoustic wave resonator implements filters with the middle two passbands than filters with the highest and lowest pass bands. Thequadplexer 80 is like the quadplexer 20 of FIG. 2A except that the BAWfilter 24 of the quadplexer 20 and the MPS filter 26 are replaced by theTCSAW filter 82 and the TCSAW filter 84, respectively, in the quadplexer80.

FIGS. 9A to 9C illustrate quadplexers with a BAW filter having a lowestpass band of the filters of the quadplexer and a SAW filter having ahighest pass band of the filters of the quadplexer. These figuresillustrate that SAW filters can be implemented in combination with oneor more BAW filters in a multiplexer in accordance with any suitableprinciples and advantages disclosed herein. The SAW filters can includewithout limitation one or more of TCSAW filters, non-temperaturecompensated SAW filters, or MPS filters.

FIG. 9A is a schematic block diagram of a quadplexer 90 according toanother embodiment. The quadplexer 90 includes a first BAW filter 22, asecond BAW filter 24, a first SAW filter 92, and a second SAW filter 94coupled together at a common node COM. The first BAW filter 22 and thesecond BAW filter 24 each include BAW resonators (e.g., FBARs and/orSMRs). In an embodiment, the acoustic wave resonators of the first BAWfilter 22 and the second BAW filter 24 consist of FBARs. The first SAWfilter 92 and the second SAW filter 94 include SAW resonators. The SAWresonators of the first SAW filter 92 and the second SAW filter 94 caninclude one or more TCSAW resonators, one or more non-temperaturecompensated SAW resonators, one or more MPS resonators, or any suitablecombination thereof. In certain applications, the quadplexer 90 can besimilar to a first duplexer that includes BAW filters 22 and 24 forfirst frequency band and a second duplexer that includes SAW filter 92and 94 for a second frequency band coupled together at the common nodeCOM, in which the second frequency band is above the first frequencyband.

The BAW filters 22 and 24 can have respective stop bands above theirpass bands. The BAW filters 22 and 24 can be a type II BAW filters thathave spurious modes below their respective resonant frequencies. The SAWfilters 26 and 28 can have respective stop bands below their pass bands.The SAW filters 26 and 28 can have spurious modes above their respectiveresonant frequencies.

FIG. 9B is a schematic block diagram of a quadplexer 95 according toanother embodiment. The quadplexer 95 is like the quadplexer 90 of FIG.9A except that SAW filter 96 is included in the quadplexer 95 in placeof the BAW filter 24 of the quadplexer 90.

FIG. 9C is a schematic block diagram of a quadplexer 97 according toanother embodiment. The quadplexer 97 is like the quadplexer 90 of FIG.9A except that BAW filter 72 is included in the quadplexer 97 in placeof the SAW filter 92 of the quadplexer 90.

Although example embodiments are discussed with duplexers andquadplexers, any suitable the principles and advantages disclosed hereincan be implement in a multiplexer that includes a plurality of filterscoupled together at a common node. Examples of multiplexers include butare not limited to a duplexer with two filters coupled together at acommon node, a triplexer with three filters coupled together at a commonnode, a quadplexer with four filters coupled together at a common node,a hexaplexer with six filters coupled together at a common node, anoctoplexer with eight filters coupled together at a common node, or thelike. A multiplexer can include (a) filters for a lower frequency bandwith spurious responses below the pass bands and (b) filters for ahigher frequency band with relatively high gamma below the pass band, inwhich the higher frequency band is above the lower frequency band. Thefilters for the lower frequency band can include a BAW filter. Thefilters for the higher frequency band can include one or more of an MPSfilter, a SAW filter, a TCSAW filter, or a type I BAW filter. Amultiplexer can include additional filters for one or more additionalfrequency bands in certain applications. FIGS. 10A and 10B illustrateexample multiplexers.

FIG. 10A is a schematic block diagram of a multiplexer 100 according toan embodiment. The multiplexer 100 includes a plurality of acoustic wavefilters coupled to a common node COM. The plurality of acoustic wavefilters can include any suitable number of filters including, forexample, 3 acoustic wave filters, 4 acoustic wave filters, 5 acousticwave filters, 6 acoustic wave filters, 7 acoustic wave filters, 8acoustic wave filters, or more acoustic wave filters. Each of theacoustic wave filters can be band pass filters. The plurality ofacoustic wave filters includes a BAW filter 102 and a SAW filter 104.The multiplexer 100 also includes one or more other acoustic wavefilters. The BAW filter 102 is coupled between a first RF node RF1 andthe common node COM. The BAW filter 102 has the lowest pass band of allacoustic wave filters of the multiplexer 100. The SAW filter 104 has thehighest pass band of all acoustic wave filters of the multiplexer 100.The SAW filter 104 can be an MPS filter, a TCSAW filter, or anon-temperature compensated SAW filter. The one or more other acousticwave filters have pass bands between the pass band of the BAW filter 102and the pass band of the SAW filter 104. The one or more other filterscan include one or more BAW filters and/or one or more SAW filters. Inthe multiplexer 100, each BAW filter of the plurality of acoustic wavefilters can have a lower pass band than a pass band of each SAW filterof the plurality of acoustic wave filters.

The multiplexer 100 can include (a) BAW filters for a lower frequencyband with spurious responses below the pass bands and (b) SAW filtersfor a higher frequency band with relatively high gamma below the passband, in which the higher frequency band is above the lower frequencyband. The multiplexer 100 can include additional filters for one or moreadditional frequency bands in certain applications.

FIG. 10B is a schematic block diagram of a multiplexer 105 according toan embodiment. The multiplexer 105 includes a plurality of BAW filterscoupled to a common node COM. The plurality of BAW filters can includeany suitable number of filters including, for example, 3 BAW filters, 4BAW filters, 5 BAW filters, 6 BAW filters, 7 BAW filters, 8 BAW filters,or more BAW filters. Each of the BAW filters can be band pass filters. Atype II BAW filter has spurious modes below its resonant frequency. Atype I BAW filter has spurious modes above its resonant frequency. Theplurality of BAW includes a type II BAW filter 106 and a type I BAWfilter 108. The multiplexer 105 also includes one or more other BAWfilters. The type II BAW filter 106 is coupled between a first RF nodeRF1 and the common node COM. The type II BAW filter 106 has the lowestpass band of all BAW filters of the multiplexer 105. The type I BAWfilter 107 has the highest pass band of all acoustic wave filters of themultiplexer 105. The one or more other BAW filters have pass bandsbetween the pass band of the type II BAW filter 106 and the pass band ofthe type I BAW filter 107. In the multiplexer 105, each type II BAWfilter of the plurality of BAW filters can have a lower pass band than apass band of each type I BAW filter of the plurality of BAW filters.

Multiplexers disclosed herein can be used to facilitate carrieraggregation. Such multiplexers can include band pass filters for atleast two different frequencies. In some instances, carrier aggregationscan aggregate carriers in two different frequency bands, three differentfrequency bands, four different frequency bands, or more frequencybands. A multiplexer can include a transmit filter and/or a receivefilter for each carrier in a carrier aggregation. As an example, for atwo band carrier aggregation, a multiplexer can include a first transmitfilter and a first receive filter for a first frequency band of a firstcarrier and a second transmit filter and a second receive filter for asecond carrier of a second frequency band. Some bands can be receiveonly or transmit only and for such filters only one filter can beincluded in a multiplexer to aggregate a carrier of that band withanother a carrier. In another example, a multiplexer can include 6filters to support a three band carrier aggregation in which there is atransmit filter and a receive filter for each of the three bands. As onemore example, a multiplexer can include 8 filters to support a four bandcarrier aggregation in which there is a transmit filter and a receivefilter for each of the four bands.

Example Long Term Evolution (LTE) frequency bands for two bandinter-band carrier aggregations, three band inter-band carrieraggregations, and four band inter-band carrier aggregations are includedin the tables below. Any suitable principles and advantages of themultiplexers disclosed herein can be implemented to support any of thecarrier aggregations identified in the tables below.

Quadplexers disclosed herein can implement inter-band carrieraggregations with two different bands. For example, the quadplexersdisclosed herein can support two band carrier aggregations with anysuitable LTE band combinations included in Tables 1A and/or 1B.

TABLE 1A Inter-Band Carrier Aggregation Combinations of 2 Bands FirstBand Second Band 1 3 1 5 1 7 1 8 1 11 1 18 1 19 1 20 1 21 1 26 1 28 1 321 38 1 40 1 41 1 42 1 43 1 46 2 4 2 5 2 7 2 12 2 13 2 14 2 17 2 28 2 292 30 2 46 2 48 2 49 2 66 2 71 2 252 2 255 3 5 3 7 3 8 3 11 3 18 3 19 320 3 21 3 26 3 27 3 28 3 31 3 32 3 38 3 40 3 41 3 42 3 43 3 46 3 69 4 54 7 4 12 4 13 4 17 4 27 4 28 4 29 4 30 4 46 4 48 4 71 4 252 4 255 5 12 513 5 17 5 25 5 28 5 29 5 30 5 38 5 40 5 41 5 46 5 48 5 66 7 8 7 12 7 207 22 7 26 7 28 7 30 7 32 7 40 7 42 7 46 7 66 8 11 8 20 8 27 8 28 8 32 838 8 39 8 40 8 41 8 42 8 46 11 18 11 26 11 28 11 41 11 42 11 46 12 25 1230 12 46 12 48 13 46 13 48 13 66 13 252 13 255 14 30 14 66 18 28 19 2119 28 19 42 19 48 20 28 20 31 20 32 20 38 20 40 20 42 20 43 20 67 20 7520 76 21 28 21 42 21 46

TABLE 1B Inter-Band Carrier Aggregation Combinations of 2 Bands(continued) First Band Second Band 23 29 25 26 25 41 25 46 26 41 26 4626 48 28 38 28 40 28 41 28 42 29 30 29 66 29 70 30 66 32 42 32 43 34 3334 41 38 40 39 40 39 41 39 42 33 46 40 41 40 42 40 43 40 46 41 42 41 4641 48 42 43 42 46 46 48 46 66 46 70 46 71 48 66 48 71 66 70 66 71 70 71

Multiplexers disclosed herein can implement inter-band carrieraggregations with three different bands. For example, a hexaplexer inaccordance with any suitable principles and advantages disclosed hereincan support three band carrier aggregations with any suitable LTE bandcombinations included in Tables 2A and/or 2B.

TABLE 2A Inter-Band Carrier Aggregation Combinations of 3 Bands FirstBand Second Band Third Band 1 3 5 1 3 7 1 3 8 1 3 11 1 3 18 1 3 19 1 320 1 3 21 1 3 26 1 3 28 1 3 32 1 3 38 1 3 40 1 3 41 1 3 42 1 3 43 1 5 71 5 40 1 5 41 1 5 46 1 7 8 1 7 20 1 7 26 1 7 28 1 7 32 1 7 40 1 7 42 1 746 1 8 11 1 8 20 1 8 28 1 8 38 1 8 40 1 11 18 1 11 28 1 18 28 1 19 21 119 28 1 19 42 1 20 28 1 20 32 1 20 42 1 20 43 1 21 28 1 21 42 1 28 42 132 42 1 32 43 1 41 42 1 42 43 2 4 5 2 4 7 2 4 12 2 4 13 2 4 28 2 4 29 24 30 2 4 71 2 5 7 2 5 12 2 5 13 2 5 28 2 5 29 2 5 30 2 5 46 2 5 66 2 712 2 7 28 2 7 30 2 7 46 2 7 66 2 12 30 2 12 66 2 13 46 2 13 48 2 13 66 214 30 2 14 66 2 29 30 2 29 66 2 30 66 2 46 48 2 46 66 2 48 66 2 66 71 35 7 3 5 40 3 5 41 3 7 8 3 7 20 3 7 26 3 7 28 3 7 32 3 7 38 3 7 40 3 7 423 7 46 3 8 11 3 8 20 3 8 28 3 8 32 3 8 38 3 8 40 3 11 18 3 11 26 3 11 283 19 21 3 19 42 3 20 28 3 20 32 3 20 42 3 20 43 3 21 28 3 21 42

TABLE 2B Inter-Band Carrier Aggregation Combinations of 3 Bands(continued) First Band Second Band Third Band 3 28 38 3 28 40 3 28 41 328 42 3 32 42 3 32 43 3 41 42 3 42 43 4 5 12 4 5 13 4 5 29 4 5 30 4 7 124 7 28 4 12 30 4 23 30 5 7 28 5 7 46 5 12 46 5 12 48 5 12 66 5 30 66 540 41 5 46 66 7 8 20 7 8 38 7 8 40 7 12 66 7 20 28 7 20 32 7 20 38 7 2042 7 28 38 7 30 66 7 46 66 8 11 28 8 20 28 8 28 41 8 33 41 12 30 66 1346 66 13 48 66 14 30 66 13 21 42 20 32 42 20 32 43 20 38 40 21 28 42 2526 41 28 41 42 23 30 66 23 46 66 23 66 70 32 42 43 46 48 66 46 48 71 6670 71

Multiplexers disclosed herein can implement inter-band carrieraggregations with four different bands. For example, an octoplexer inaccordance with any suitable principles and advantages disclosed hereincan support four band carrier aggregations with any suitable LTE bandcombinations included in Table 3.

TABLE 3 Inter-Band Carrier Aggregation Combinations of 4 Bands FirstBand Second Band Third Band Fourth Band 1 3 5 7 1 3 5 40 1 3 5 41 1 3 78 1 3 7 20 1 3 7 26 1 3 7 28 1 3 7 32 1 3 7 40 1 3 7 42 1 3 8 11 1 3 820 1 3 8 28 1 3 8 38 1 3 8 40 1 3 11 28 1 3 19 21 1 3 19 42 1 3 20 28 13 20 32 1 3 20 42 1 3 20 43 1 3 21 28 1 3 21 42 1 3 28 42 1 3 32 42 1 332 43 1 3 42 43 1 5 7 46 1 7 8 20 1 7 8 40 1 7 20 28 1 7 20 32 1 7 20 421 8 11 28 1 8 20 28 1 19 21 42 1 20 32 42 1 20 32 43 1 21 28 42 1 32 4243 2 4 5 12 2 4 5 29 2 4 5 30 2 4 7 12 2 4 12 30 2 4 29 30 2 5 7 28 2 512 66 2 5 30 66 2 7 12 66 2 7 46 66 2 12 30 66 2 13 48 66 2 14 30 66 229 30 66 2 46 48 66 3 7 8 20 3 7 8 38 3 7 8 40 3 7 20 28 3 7 20 32 3 720 42 3 7 28 38 3 8 11 28 3 8 20 28 3 19 21 42 3 20 32 42 3 20 32 43 321 28 42 3 28 41 42 3 32 42 43

A multiplexer including any suitable combination of features disclosedherein can include one or more filters arranged to filter a radiofrequency signal in a fifth generation (5G) New Radio (NR) operatingband within Frequency Range 1 (FR1). FR1 can be from 410 MHz to 7.125GHz, for example, as specified in a current 5G NR specification. Amultiplexer in accordance with any suitable principles and advantagesdisclosed herein can support any suitable 5G NR carrier aggregationswithin FR1. A multiplexer with a filter having a relatively high gammain a passband of one or more other filters of the multiplexer can beadvantageous for meeting specifications related to 5G NR technology. Asone example, such a multiplexer can be advantageous for 5G NR carrieraggregation applications. In 5G applications, the thermal dissipation ofMPS acoustic wave resonators in filters of multiplexers disclosed hereincan be advantageous. One or more acoustic wave filters in multiplexersdisclosed herein can have a passband that includes a 4G LTE operatingband and a 5G NR operating band.

FIG. 11A is a cross sectional view of a multilayer piezoelectricsubstrate (MPS) SAW resonator 110 according to an embodiment. The MPSSAW resonator 110 is an example of a resonator of the MPS filtersdisclosed herein. The MPS filters disclosed herein can include anysuitable number of MPS SAW resonators, such as the MPS SAW resonator110. The illustrated MPS SAW resonator 110 includes a multilayerpiezoelectric substrate includes a piezoelectric substrate 112 and asupport substrate 114. The piezoelectric substrate 112 can be a lithiumniobate substrate or a lithium tantalate substrate, for example. Incertain instances, the piezoelectric layer 114 can have a thickness ofless than A, in which A is a wavelength of a surface acoustic wavegenerated by the MPS SAW resonator 110. In some other instances, thepiezoelectric layer 114 can have a thickness on the order of 10s of λ,in which λ is a wavelength of a surface acoustic wave generated by theMPS SAW resonator 110. The thickness of the piezoelectric layer 114 canbe in a range from about 20 microns to 30 microns in certainapplications. The support substrate 114 can be a silicon substrate, aquartz substrate, a sapphire substrate, a polycrystalline spinelsubstrate, or any other suitable carrier substrate. As one example, theMPS SAW resonator 110 can include a piezoelectric substrate 112 that islithium tantalate and a support substrate 114 that is silicon. The MPSSAW resonator 110 also includes an interdigital transducer (IDT)electrode 115 on the piezoelectric substrate 112.

In some instances, one or more additional layers can be included in themultilayer piezoelectric substrate. Non-limiting examples of a layer ofthe one or more additional layers include a silicon dioxide layer, asilicon nitride layer, an aluminum nitride layer, an adhesion layer, adispersion adjustment layer, and a thermal dissipation layer. As anillustrative example, a multilayer piezoelectric substrate can include alithium tantalate layer over a silicon dioxide layer over an aluminumnitride layer over a silicon layer. As one more illustrative example, amultilayer piezoelectric substrate can include a lithium niobate layerover a silicon dioxide layer over a high impedance layer, in which thehigh impedance layer has a higher acoustic impedance than the lithiumniobate layer.

In some instances, a temperature compensation layer can be implementedover the IDT electrode 115. Such a temperature compensation layer canbring the temperature coefficient of frequency of the MPS SAW resonatorcloser to zero. As an example, a silicon dioxide layer can implement atemperature compensation layer.

FIG. 11B is a cross sectional view of a SAW resonator 116 according toan embodiment. The SAW resonator 116 is an example of a resonator of SAWfilters disclosed herein. The SAW resonator 116 is an example of anon-temperature compensated SAW resonator. In certain applications, SAWfilters disclosed herein can include any suitable number ofnon-temperature compensated SAW resonators, such as the SAW resonator116. The illustrated SAW resonator 116 includes a piezoelectricsubstrate 112 and an IDT electrode 115 on the piezoelectric substrate112. The piezoelectric substrate 112 can be a lithium niobate substrateor a lithium tantalate substrate, for example.

FIG. 11C is a cross sectional view of a TCSAW resonator 118 according toan embodiment. The TCSAW resonator 118 is an example of a resonator ofTCSAW filters disclosed herein. In certain applications, TCSAW filtersdisclosed herein can include any suitable number of TCSAW resonators,such as the TCSAW resonator 118. The illustrated TC SAW resonator 118includes a piezoelectric substrate 112, an IDT electrode 115 on thepiezoelectric substrate 112, and a temperature compensation layer 119over the IDT electrode 115. The piezoelectric substrate 112 can be alithium niobate substrate or a lithium tantalate substrate, for example.

The temperature compensation layer 119 can bring the temperaturecoefficient of frequency (TCF) of the TCSAW resonator 118 closer to zerorelative to a similar SAW resonator without the temperature compensationlayer 119. The temperature compensation layer 119 can have a positiveTCF. This can compensate for the piezoelectric substrate 112 having anegative TCF. The temperature compensation layer 119 can be a silicondioxide (SiO₂) layer. The temperature compensation layer 119 can be anyother suitable temperature compensating material including withoutlimitation a tellurium dioxide (TeO₂) layer or a silicon oxyfluoride(SiOF layer). The temperature compensation layer 119 can include anysuitable combination of SiO₂, TeO₂, and/or SiOF.

FIG. 12 is a cross sectional view of a BAW resonator 120 according to anembodiment. The BAW resonator 120 is an example of a resonator of BAWfilters disclosed herein. In certain applications, BAW filters disclosedherein can include any suitable number of BAW resonators, such as theBAW resonator 120. The BAW resonator 120 is an FBAR. The BAW resonator120 can be a type II BAW resonator.

As illustrated, the BAW resonator 120 includes a piezoelectric layer122, a first electrode 123, and a second electrode 124, a supportsubstrate 125, and an air gap 126. The piezoelectric layer 122 isdisposed between the first electrode 123 and the second electrode 124.The piezoelectric layer 122 can be an aluminum nitride (AlN) layer orany other suitable piezoelectric layer. An active region or activedomain of the BAW resonator 120 is defined by the portion of thepiezoelectric layer 122 that overlaps with both the first electrode 123and the second electrode 124. The first electrode 123 can have arelatively high acoustic impedance. For example, the first electrode 123can include molybdenum, tungsten, ruthenium, iridium, platinum, copper,gold, or any suitable combination thereof. Similarly, the secondelectrode 124 can have a relatively high acoustic impedance. The secondelectrode 124 can be formed of the same material as the first electrode123 in certain instances. The air gap 126 is included between thesubstrate 125 and the second electrode 124. The illustrated air gap 126is an air cavity above the substrate 125. In some other instances (notillustrated), an air cavity in the substrate 125 can alternatively beimplemented. The substrate 125 can be a silicon substrate, for example.

Acoustic wave filters disclosed herein can have a ladder filtertopology. FIG. 13 is a schematic diagram of an example ladder filter 130according to an embodiment. The ladder filter 130 is an example topologyof the band pass filter formed from acoustic wave resonators that can beincluded in a multiplexer in accordance with any suitable principles andadvantages disclosed herein. The ladder filter 130 can be arranged tofilter an RF signal. As illustrated, the ladder filter 130 includesseries acoustic wave resonators 131, 133, 135, 137, and 139 and shuntacoustic wave resonators 132, 134, 136, and 138 coupled between an RFport RF and an antenna port ANT. The RF port can be a transmit port fora transmit filter or a receive port for a receive filter. Any suitablenumber of series acoustic resonators can be in included in a ladderfilter. Any suitable number of shunt acoustic wave resonators can beincluded in a ladder filter. Any of the illustrated acoustic waveresonators can be implemented by a plurality of series acoustic waveresonators and/or anti-series acoustic wave resonators and/or shuntacoustic wave resonators.

The multiplexers discussed herein can be implemented in a variety ofradio frequency systems. Multiplexers disclosed herein process radiofrequency signals having frequencies in a range from about 450 MHz to 6GHz and/or in a range from about 410 MHz to 7.125 GHz. In certainapplications, multiplexers disclosed herein can filter radio frequencysignals at up to about 10 GHz. Some radio frequency systems that includemultiplexers in accordance with the principles and advantages discussedherein are configured to process carrier aggregation signals. In radiofrequency systems with carrier aggregation, multiple filters can bearranged as a multiplexer and connected to a common antenna node. Someexample radio frequency systems will be discussed with reference toFIGS. 14, 15, 16, 17A, and 17B in which any suitable principles andadvantages of the multiplexers disclosed herein can be implemented.

FIG. 14 is a schematic diagram of a radio frequency system 140 thatincludes quadplexers 142 and 144 coupled to an antenna 146 by way of adiplexer 146. The first quadplexer 142 and/or the second quadplexer 144can be implemented in accordance with any suitable principles andadvantages of the multiplexers disclosed herein. In FIG. 14, a firstquadplexer 142 includes four acoustic wave filters each arranged as aband pass filter configured to filter a radio frequency signal. The fouracoustic wave filters include two transmit filters and two receivefilters. In FIG. 14, a second quadplexer 144 also includes four acousticwave filters similar to the acoustic wave filters of the firstquadplexer 142 but associated with different frequency bands. Thediplexer 145 can frequency multiplex radio frequency signals propagatingbetween the illustrated quadplexers 142 and 144 and the antenna 146. Thediplexer 146 can allow lower frequency signals to propagate between thefirst quadplexer 142 and the antenna 146, and the diplexer 145 can allowhigher frequency signals to propagate between the second quadplexer 144and the antenna 146.

FIG. 15 is a schematic diagram of a radio frequency system 150 thatincludes a quadplexer 142 coupled to an antenna 146. FIG. 15 illustratesthat a multiplexer in accordance with any suitable principles andadvantages disclosed herein can be connected to an antenna without anintervening frequency multiplexing circuit (e.g., a diplexer or atriplexer) in some applications. For instance, when a carrieraggregation signal includes two carriers that are relatively close infrequency, a diplexer or a triplexer can be relatively difficult and/orexpensive to implement and/or have relatively high loss. In suchcircumstances, filters can be connected together at a common node as amultiplexer. As one example, such a multiplexer can be a quadplexer withtransmit and receive filters for Band 25 and Band 66. A multiplexer canbe connected to an antenna without an intervening switch or frequencymultiplexing circuit in certain applications, as shown in FIG. 15. Forinstance, a mobile phone configured for wireless communication of acarrier aggregation signal with only two carrier aggregation bands caninclude a multiplexer having a multiplexer connected to an antennawithout any intervening switch or frequency multiplexing circuit.

FIG. 16 is a schematic diagram of a radio frequency system 160 thatincludes an antenna 162 coupled to receive paths 165 and 166 by way of amultiplexer. In some instances, a radio can be implemented for diversityreceive operations. A diversity antenna, such as the illustrated antenna162, can provide a received radio frequency signal to several receivepaths. A multiplexer in accordance with any suitable principles andadvantages disclosed herein can be coupled between a plurality ofreceive paths 165 and 166 and the diversity antenna 162. As shown inFIG. 16, a multiplexer (e.g., a quadplexer) including receive filters163 and 164 can be coupled between receive paths 165 and 164,respectively, and the antenna 162. Any suitable number of receive pathsand corresponding receive filters can be implemented for a particularimplementation. For instance, 4 or more receive filters can be includedin a multiplexer and respective receive paths in some instances. In someembodiments (not illustrated), a switch can be coupled between amultiplexer and a diversity antenna and/or a switch can be coupledbetween receive paths and a receive filter of the multiplexer.

FIG. 17A is a schematic diagram of a radio frequency system 170 thatincludes multiplexers in signal paths between power amplifiers and anantenna. The illustrated radio frequency system 170 includes a low bandpath, a medium band path, and a high band path. In certain applications,a low band path can process radio frequency signals having a frequencyof less than 1 GHz, a medium band path can process radio frequencysignals having a frequency between 1 GHz and 2.2 GHz, and a high bandpath can process radio frequency signals having a frequency above 2.2GHz. Any of the multiplexers 173, 176, and 179 of the radio frequencysystem 170 can be implemented in accordance with any suitable principlesand advantages disclosed herein.

A frequency multiplexing circuit, such as a diplexer 145, can beincluded between signal paths and the antenna 146. Such a frequencymultiplexing circuit can serve as a frequency splitter for receive pathsand a frequency combiner for transmit paths. The diplexer 145 canfrequency multiplex radio frequency signals that are relatively far awayin frequency. The diplexer 145 can be implemented with passive circuitelements having a relatively low loss. The diplexer 145 can combine (fortransmit) and separate (for receive) carrier aggregation signals.

As illustrated, the low band path includes a power amplifier 171configured to amplify a low band radio frequency signal, a band selectswitch 172, and a multiplexer 173. The band select switch 172 canelectrically connect the output of the power amplifier 171 to a selectedtransmit filter of the multiplexer 173. The selected transmit filter canbe a band pass filter with a pass band corresponding to a frequency ofan output signal of the power amplifier 171. The multiplexer 173 caninclude any suitable number of transmit filters and any suitable numberof receive filters. The multiplexer 173 can have the same number oftransmit filters as receive filters in certain applications. In someinstances, the multiplexer 173 can have a different number of transmitfilters than receive filters.

As illustrated in FIG. 17A, the medium band path includes a poweramplifier 174 configured to amplify a medium band radio frequencysignal, a band select switch 175, and a multiplexer 176. The band selectswitch 175 can electrically connect the output of the power amplifier174 to a selected transmit filter of the multiplexer 176. The selectedtransmit filter can be a band pass filter with a pass band correspondingto a frequency of an output signal of the power amplifier 174. Themultiplexer 176 can include any suitable number of transmit filters andany suitable number of receive filters. The multiplexer 176 can have thesame number of transmit filters as receive filters in certainapplications. In some instances, the multiplexer 176 can have adifferent number of transmit filters than receive filters.

In the illustrated radio frequency system 170, the high band pathincludes a power amplifier 177 configured to amplify a high band radiofrequency signal, a band select switch 178, and a multiplexer 179. Theband select switch 178 can electrically connect the output of the poweramplifier 177 to a selected transmit filter of the multiplexer 179. Theselected transmit filter can be a band pass filter with pass bandcorresponding to a frequency of an output signal of the power amplifier177. The multiplexer 179 can include any suitable number of transmitfilters and any suitable number of receive filters. The multiplexer 179can have the same number of transmit filters as receive filters incertain applications. In some instances, the multiplexer 179 can have adifferent number of transmit filters than receive filters.

A select switch 180 can selectively provide a radio frequency signalfrom the medium band path or the high band path to the diplexer 145.Accordingly, the radio frequency system 170 can process carrieraggregation signals with either a low band and high band combination ora low band and medium band combination.

FIG. 17B is a schematic diagram of another radio frequency system 182that includes multiplexers in signal paths between power amplifiers andan antenna. Any of the multiplexers 173, 183, and 184 of the radiofrequency system 170 can be implemented in accordance with any suitableprinciples and advantages disclosed herein. The radio frequency system182 is like the radio frequency system 170 of FIG. 17A, except that theradio frequency system 182 includes switch-plexing features.Switch-plexing can be implemented in accordance with any suitableprinciples and advantages discussed herein.

Switch-plexing can implement on-demand multiplexing. Some radiofrequency systems can operate in a single carrier mode for a majority oftime (e.g., about 95% of the time) and in a carrier aggregation mode fora minority of the time (e.g., about 5% of the time). Switch-plexing canreduce loading in a single carrier mode in which the radio frequencysystem can operate for the majority of the time relative to amultiplexer that includes filters having a fixed connection at a commonnode. Such a reduction in loading can be more significant when there area larger number of filters included in multiplexer.

In the illustrated radio frequency system 182, multiplexers 183 and 184are coupled to a diplexer 176 by way of a switch 185. The switch 185 isconfigured as a multi-close switch that can have two or more throwsactive concurrently. Having multiple throws of the switch 185 activeconcurrently can enable transmission and/or reception of carrieraggregation signals. The switch 185 can also have a single throw activeduring a single carrier mode. As illustrated, the multiplexer 183includes a plurality of duplexers coupled to separate throws of theswitch 185. Similarly, the illustrated multiplexer 184 includes aplurality of duplexers coupled to separate throws of the switch 185.Alternatively, instead of duplexers being coupled to each throw theswitch 185 as illustrated in FIG. 17B, one or more individual filters ofa multiplexer can be coupled to a dedicated throw of a switch coupledbetween the individual filters and a common node. For instance, in someapplications, such a switch could have twice as many throws as theillustrated switch 185.

The switch 185 is coupled between filters of the multiplexers 183 and184, respectively, and a common node COM. FIG. 17B illustrates that lessthan all of the filters of a multiplexer can be electrically connectedto the common node concurrently.

In some instances, two or more throws of a switch coupled between apower amplifier and a multiplexer can be active concurrently. Forexample, in the radio frequency system 182, two or more throws of theband select switch 175 and/or the band select switch 178 can be activeconcurrently in certain embodiments.

FIG. 18A is a block diagram of a filter assembly 190 with different diethat include acoustic wave resonators of filters according to anembodiment. As illustrated, the filter assembly 190 includes a SAW die191 and a BAW die 192 that are included on a common substrate 193. Amultiplexer in accordance with any suitable principles and advantagesdisclosed herein can include one filter with SAW resonators implementedon the SAW die 191 and another filter with BAW resonators implemented onthe BAW die 192. The BAW resonators can be FBARs according to certainembodiments. The BAW resonators can be type II BAW resonators. The SAWresonators can be MPS SAW resonators in certain embodiments. Accordingto some other embodiments, the SAW resonators can include TCSAWresonators and/or non-temperature compensated SAW resonators. Thesubstrate 193 can be a laminate substrate or any other suitablepackaging substrate.

In certain instances, the BAW die 192 includes a single filter and theSAW die 191 includes a single filter. As one example, BAW resonators ofthe BAW die 192 can be arranged as the BAW filter 12 of the duplexer 10of FIG. 1A and MPS SAW resonators of the SAW die 191 can be arranged asthe MPS filter 14 of the duplexer 10 of FIG. 1A. In some otherinstances, the BAW die 192 includes a single filter and the SAW die 191includes two or more filters. For example, BAW resonators of the BAW die192 can be arranged as the BAW filter 22 of the quadplexer 73 of FIG. 7Band MPS SAW resonators of the SAW die 191 can be arranged as at leasttwo of the MPS filters 26, 28, and 74 of the quadplexer 73 of FIG. 7B.

FIG. 18B is a block diagram of a filter assembly 194 with different diethat include acoustic wave resonators of filters according to anembodiment. As illustrated, the filter assembly 194 includes a SAW die191, a first BAW die 192, and a second BAW die 195 on a common substrate193. A multiplexer in accordance with any suitable principles andadvantages disclosed herein can include filters implemented on the SAWdie 191, the first BAW die 192, and the second BAW die 195. For example,a triplexer can include a first filter on the first BAW die 192, asecond filter on the second BAW die 195, and a third filter on the SAWdie 191. In this example, the first filter can have the lowest passbandand the third filter can have the highest passband. As another example,a quadplexer can include a first filter on the first BAW die 192, asecond filter on the second BAW die 195, a third filter on the SAW die191, and a fourth filter on the SAW die 191. In this example, the firstfilter can have the lowest passband, the second filter can have the nextlowest passband, the third filter can have the next lowest passband, andthe fourth filter can have the highest passband. Such a quadplexer canimplement any suitable combination of features of the quadplexer 20 ofFIG. 2A and/or the quadplexer 90 of FIG. 9A.

FIG. 18C is a block diagram of a filter assembly 196 with different diethat include acoustic wave resonators of filters according to anembodiment. As illustrated, the filter assembly 196 includes a first SAWdie 191, a second SAW die 197, a first BAW die 192, and a second BAW die195 on a common substrate 193. A multiplexer in accordance with anysuitable principles and advantages disclosed herein can include filtersimplemented on the first SAW die 191, the second SAW die 197, the firstBAW die 192, and the second BAW die 195. For example, a quadplexer caninclude a first filter on the first BAW die 192, a second filter on thesecond BAW die 195, a third filter on the first SAW die 191, and afourth filter on the second SAW die 197. In this example, the firstfilter can have the lowest passband, the second filter can have the nextlowest passband, the third filter can have the next lowest passband, andthe fourth filter can have the highest passband. Such a quadplexer canimplement any suitable combination of features of the quadplexer 20 ofFIG. 2A and/or the quadplexer 90 of FIG. 9A.

The multiplexers discussed herein can be implemented in a variety ofpackaged modules. Some example packaged modules will now be discussed inwhich any suitable principles and advantages of the multiplexers can beimplemented. FIGS. 19 and 20 are schematic block diagrams ofillustrative packaged modules according to certain embodiments.

FIG. 19 is a schematic block diagram of a module 200 that includes apower amplifier 201, a switch 202, and a multiplexer 203 according to anembodiment. The module 200 can include a package that encloses theillustrated elements. In some instances, the package can enclosedadditional circuit elements. The power amplifier 201, the switch 202,and the multiplexer 203 can be disposed on a common packaging substrate.The packaging substrate can be a laminate substrate, for example. Theswitch 202 can be a multi-throw radio frequency switch. The switch 202can electrically couple an output of the power amplifier 201 to aselected transmit filter of the multiplexer 203. The switch 202 canelectrically couple an input of a low noise amplifier (not illustrated)to a selected receive filter of the multiplexer 203. The low noiseamplifier can be included in the module 200 in some instances. Accordingto some other instances, the low noise amplifier can be external to themodule 200. The multiplexer 203 can include any suitable features of themultiplexers disclosed herein.

FIG. 20 is a schematic block diagram of a module 204 that includes poweramplifiers 201 and 205, switches 202 and 206, and a multiplexer 207according to an embodiment. The multiplexer 207 can implement anysuitable combination of features of the multiplexers disclosed herein.The module 204 is like the module 200 of FIG. 19, except that the module204 includes an addition power amplifier 204 and an additional switch206 and the multiplexer 207 can receive signals from the poweramplifiers 201 and 205. The switches 202 and 206 can concurrently coupleoutputs of the power amplifiers 201 and 205, respectively, to differenttransmit filters of the multiplexer 207. The switches 202 and 206 canconcurrently couple inputs of low noise amplifiers (not illustrated) todifferent receive filters of the multiplexer 207.

FIG. 21A is a schematic diagram of a wireless communication 210 devicethat includes multiplexer(s) 213 in a radio frequency front end 212according to an embodiment. The multiplexer(s) 213 can be implemented inaccordance with any suitable principles and advantages discussed herein.The wireless communication device 210 can be any suitable wirelesscommunication device. For instance, a wireless communication device 210can be a mobile phone, such as a smart phone. As illustrated, thewireless communication device 210 includes an antenna 211, an RF frontend 212, a transceiver 214, a processor 215, a memory 216, and a userinterface 217. The antenna 211 can transmit RF signals provided by theRF front end 212. Such RF signals can include carrier aggregationsignals. The antenna 211 can receive RF signals and provide the receivedRF signals to the RF front end 212 for processing. Such RF signals caninclude carrier aggregation signals.

The RF front end 212 can include one or more power amplifiers, one ormore low noise amplifiers, one or more RF switches, one or more receivefilters, one or more transmit filters, one or more duplex filters, oneor more multiplexers, one or more frequency multiplexing circuits, thelike, or any suitable combination thereof. The RF front end 212 cantransmit and receive RF signals associated with any suitablecommunication standards. The multiplexer(s) 213 can include any suitablecombination of features discussed with reference to any embodimentsdiscussed above.

The transceiver 214 can provide RF signals to the RF front end 212 foramplification and/or other processing. The transceiver 214 can alsoprocess an RF signal provided by a low noise amplifier of the RF frontend 212. The transceiver 214 is in communication with the processor 215.The processor 215 can be a baseband processor. The processor 215 canprovide any suitable base band processing functions for the wirelesscommunication device 210. The memory 216 can be accessed by theprocessor 215. The memory 216 can store any suitable data for thewireless communication device 210. The user interface 217 can be anysuitable user interface, such as a display with touch screencapabilities.

FIG. 21B is a schematic diagram of a wireless communication device 220that includes multiplexer(s) 213 in a radio frequency front end 212 andsecond filters 223 in a diversity receive module 222. The wirelesscommunication device 220 is like the wireless communication device 210of FIG. 21A, except that the wireless communication device 220 alsoincludes diversity receive features. As illustrated in FIG. 21B, thewireless communication device 220 includes a diversity antenna 221, adiversity module 222 configured to process signals received by thediversity antenna 221 and including multiplexer(s) 223, and atransceiver 224 in communication with both the radio frequency front end212 and the diversity receive module 222. The multiplexer(s) 223 caninclude any suitable combination of features discussed with reference toany embodiments discussed above.

Any of the embodiments described above can be implemented in associationwith mobile devices such as cellular handsets. The principles andadvantages of the embodiments can be used for any systems or apparatus,such as any uplink wireless communication device, that could benefitfrom any of the embodiments described herein. The teachings herein areapplicable to a variety of systems. Although this disclosure includesexample embodiments, the teachings described herein can be applied to avariety of structures. Any of the principles and advantages discussedherein can be implemented in association with RF circuits configured toprocess signals having a frequency in a range from about 30 kHz to 300GHz, such as in a frequency range from about 400 MHz to 8.5 GHz.Acoustic wave filters disclosed herein can filter RF signals atfrequencies up to and including millimeter wave frequencies.

Aspects of this disclosure can be implemented in various electronicdevices. Examples of the electronic devices can include, but are notlimited to, consumer electronic products, parts of the consumerelectronic products such as packaged radio frequency modules, uplinkwireless communication devices, wireless communication infrastructure,electronic test equipment, etc. Examples of the electronic devices caninclude, but are not limited to, a mobile phone such as a smart phone, awearable computing device such as a smart watch or an ear piece, atelephone, a television, a computer monitor, a computer, a modem, ahand-held computer, a laptop computer, a tablet computer, a microwave, arefrigerator, a vehicular electronics system such as an automotiveelectronics system, a robot such as an industrial robot, an Internet ofthings device, a stereo system, a digital music player, a radio, acamera such as a digital camera, a portable memory chip, a homeappliance such as a washer or a dryer, a peripheral device, a wristwatch, a clock, etc. Further, the electronic devices can includeunfinished products.

Unless the context indicates otherwise, throughout the description andthe claims, the words “comprise,” “comprising,” “include,” “including”and the like are to generally be construed in an inclusive sense, asopposed to an exclusive or exhaustive sense; that is to say, in thesense of “including, but not limited to.” Conditional language usedherein, such as, among others, “can,” “could,” “might,” “may,” “e.g.,”“for example,” “such as” and the like, unless specifically statedotherwise, or otherwise understood within the context as used, isgenerally intended to convey that certain embodiments include, whileother embodiments do not include, certain features, elements and/orstates. The word “coupled”, as generally used herein, refers to two ormore elements that may be either directly connected, or connected by wayof one or more intermediate elements. Likewise, the word “connected”, asgenerally used herein, refers to two or more elements that may be eitherdirectly connected, or connected by way of one or more intermediateelements. Additionally, the words “herein,” “above,” “below,” and wordsof similar import, when used in this application, shall refer to thisapplication as a whole and not to any particular portions of thisapplication. Where the context permits, words in the above DetailedDescription using the singular or plural number may also include theplural or singular number respectively.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the disclosure. Indeed, the novel resonators, devices, modules,apparatus, methods, and systems described herein may be embodied in avariety of other forms. Furthermore, various omissions, substitutionsand changes in the form of the resonators, devices, modules, apparatus,methods, and systems described herein may be made without departing fromthe spirit of the disclosure. For example, while blocks are presented ina given arrangement, alternative embodiments may perform similarfunctionalities with different components and/or circuit topologies, andsome blocks may be deleted, moved, added, subdivided, combined, and/ormodified. Each of these blocks may be implemented in a variety ofdifferent ways. Any suitable combination of the elements and/or acts ofthe various embodiments described above can be combined to providefurther embodiments. The accompanying claims and their equivalents areintended to cover such forms or modifications as would fall within thescope and spirit of the disclosure.

What is claimed is:
 1. A multiplexer with acoustic wave filters forfiltering radio frequency signals, the multiplexer comprising: a firstacoustic wave filter coupled to a common node and having a first passband, the first acoustic wave filter including bulk acoustic waveresonators; a second acoustic wave filter coupled to the common node andhaving a second pass band; a third acoustic wave filter coupled to thecommon node and having a third pass band; and a fourth acoustic wavefilter coupled to the common node and having a fourth pass band, thefourth acoustic wave filter including surface acoustic wave resonators,the first pass band having a lower pass band than the second, third andfourth acoustic wave filters.
 2. The multiplexer of claim 1 wherein thefourth pass band is a highest pass band of the first, second and thirdacoustic wave filters.
 3. The multiplexer of claim 1 wherein the surfaceacoustic wave resonators include multilayer piezoelectric substratesurface acoustic wave resonators.
 4. The multiplexer of claim 1 whereinthe first acoustic wave filter and third acoustic wave filter eachinclude multilayer piezoelectric substrate surface acoustic waveresonators.
 5. The multiplexer of claim 1 wherein the surface acousticwave resonators include temperature compensated surface acoustic waveresonators.
 6. The multiplexer of claim 1 wherein the second acousticwave filter includes second bulk acoustic wave resonators, the thirdacoustic wave filter includes second surface acoustic wave resonators,and the second pass band being below the third pass band.
 7. Themultiplexer of claim 1 wherein the second acoustic wave filter includessecond bulk acoustic wave resonators, the third acoustic wave filterincludes third bulk acoustic wave resonators, and the second pass bandis below the third pass band.
 8. The multiplexer of claim 1 wherein thesecond acoustic wave filter includes second surface acoustic waveresonators, the third acoustic wave filter includes third surfaceacoustic wave resonators, and the second pass band is below the thirdpass band.
 9. The multiplexer of claim 1 wherein the multiplexer isconfigured to support a carrier aggregation of at least two frequencybands.
 10. The multiplexer of claim 1 wherein the multiplexer isconfigured to support a carrier aggregation of at least three frequencybands.
 11. The multiplexer of claim 1 wherein the bulk acoustic waveresonators have spurious modes below the first pass band.
 12. Themultiplexer of claim 1 wherein the surface acoustic wave resonators havea gamma of at least 0.85 in the first pass band.
 13. The multiplexer ofclaim 1 wherein spurious modes of the bulk acoustic wave resonators areoutside of the fourth pass band.
 14. The multiplexer of claim 1 whereinthe bulk acoustic wave resonators have a substantially constant gamma inthe fourth pass band.
 15. A wireless communication device comprising: anantenna; and a radio frequency front end including a multiplexer incommunication with the antenna, the multiplexer including: a firstacoustic wave filter coupled to a common node and having a first passband, the first acoustic wave filter including bulk acoustic waveresonators; a second acoustic wave filter coupled to the common node andhaving a second pass band; a third acoustic wave filter coupled to thecommon node and having a third pass band; and a fourth acoustic wavefilter coupled to the common node and having a fourth pass band, thefourth acoustic wave filter including surface acoustic wave resonators,the first pass band having a lower pass band than the second, third andfourth acoustic wave filters.
 16. The wireless communication device ofclaim 15 wherein the radio frequency front end includes a frequencymultiplexing circuit coupled between the common node of the multiplexerand the antenna.
 17. The wireless communication device of claim 15further comprising an antenna switch coupled between the common node ofthe multiplexer and the antenna.
 18. A packaged radio frequency modulecomprising: a multiplexer including: a first acoustic wave filtercoupled to a common node and having a first pass band, the firstacoustic wave filter including bulk acoustic wave resonators; a secondacoustic wave filter coupled to the common node and having a second passband; a third acoustic wave filter coupled to the common node and havinga third pass band; and a fourth acoustic wave filter coupled to thecommon node and having a fourth pass band, the fourth acoustic wavefilter including surface acoustic wave resonators, the first pass bandhaving a lower pass band than the second, third and fourth acoustic wavefilters; a multi-throw radio frequency switch coupled to themultiplexer; and a package enclosing the multiplexer and the multi-throwradio frequency switch.
 19. The packaged radio frequency module of claim18 further comprising a power amplifier enclosed within the package, thepower amplifier configured to provide a radio frequency signal to themultiplexer.
 20. The packaged radio frequency module of claim 18 furthercomprising a low noise amplifier enclosed within the package, the lownoise amplifier configured to receive a radio frequency signal to themultiplexer.